linux-kernel - Re: [PATCH v5] MIPS: Truncate link address into 32bit for 32bit kernel

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Message-ID: <alpine.LFD.2.21.2004241316360.851719@eddie.linux-mips.org>
Date:   Fri, 24 Apr 2020 13:22:30 +0100 (BST)
From:   "Maciej W. Rozycki" <macro@...ux-mips.org>
To:     Jiaxun Yang <jiaxun.yang@...goat.com>
cc:     linux-mips@...r.kernel.org, clang-built-linux@...glegroups.com,
        Fangrui Song <maskray@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Nathan Chancellor <natechancellor@...il.com>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Paul Burton <paulburton@...nel.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Jouni Hogander <jouni.hogander@...kie.com>,
        Kevin Darbyshire-Bryant <ldir@...byshire-bryant.me.uk>,
        Borislav Petkov <bp@...e.de>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5] MIPS: Truncate link address into 32bit for 32bit
 kernel

On Thu, 23 Apr 2020, Jiaxun Yang wrote:

> > Alternatively, have you made any attempt to verify if actually replacing 
> >the setting for VMLINUX_LOAD_ADDRESS would be safe?  Glancing over its use 
> >there do not appear to be many places.
> 
> Limited experiments showed it should be fine...
> 
> But MIPS kernel has some design I'm not really familiar with like SYM32 for
> 64-bit kernel and special address space design for Trap-and-emul KVM.

 This only affects CONFIG_32BIT kernels, so SYM32 does not apply; I can't 
comment on KVM.  There's still that bunch of:

$(shell expr $(...) \< 0xffffffff80000000)

constructs I mentioned before, so let's leave your change as it stands at 
this time.  Please do rename the variable as I suggested though, I hope 
that's not a big deal.

  Maciej